Question

Why hot water has less dissolved air than cold water?

Answer 1

Here is ur answer

The amount of dissolved oxygen that the water can hold depends on the temperature and salinity of the water.Cold water can hold more dissolvedoxygen than warm water and freshwater can hold more dissolved oxygenthan salt water. So the warmer and saltier the water, the less dissolvedoxygen there can be.

Answer 2

Oxygen is only slightly soluble in water.
At higher temperature, the O2 molecules have greater amount of kinetic energy than that in cold water. So the gas molecules in hot water can more easily overcome the weak binding forces within water and escape through the surface.